Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $239.39   12.435%   $269.1581   $269.16   $269.15   $269.20  
  Purchase #2 $54.67   4.761%   $57.2728   $57.27   $57.25   $57.30  
  Purchase #3 $14.53   10.854%   $16.1071   $16.11   $16.10   $16.10  
  Purchase #4 $99.29   8.852%   $108.0792   $108.08   $108.10   $108.10  
  Purchase #5 $237.87   3.754%   $246.7996   $246.80   $246.80   $246.80  
  Purchase #6 $194.64   3.457%   $201.3687   $201.37   $201.35   $201.40  
  Purchase #7 $125.88   7.316%   $135.0894   $135.09   $135.10   $135.10  
  7 purchase totals = $966.27       $1,033.8749   $1,033.88   $1,033.85   $1,034.00